Composition and method for making magnetic recording elements

Abstract

A composition for making magnetic recording elements comprising finely divided particles of magnetic pigment dispersed in an organic medium comprising polymeric binder, lubricant, dispersing agent and porosity control agent dispersed in volatile organic solvent.

We claim: 
     
       1. A method for manufacturing magnetic recording elements which comprises the sequential steps of a. coating onto a surface of a nonmagnetic carrier a layer of a composition which comprises (1) finely divided particles of magnetic particles dispersed in a liquid medium comprising   (2) film-forming polymeric binder,   (3) 0.2-20% wt. lubricant, basis solvent-free layer,   (4) 0.5-6% wt. dispersing agent, basis magnetic pigment, and   (5) porosity control agent selected from metal salts of carboxylic acids, nonionogenic diurethanes, calcium-containing micellar organic complexes and mixtures thereof, all of (2) through (5) being dispersed in   (6) volatile organic solvent:     b. removing essentially all of the volatile organic solvent by evaporation from the coated layer;   c. compressing the solvent-free coated layer, thus forming in the layer a structure of pores having a diameter of 5-100 nm, a pore volume which is 5-50% of the volume of the compressed layer, and a pore surface area which is at least 100 times the free surface area of the compressed layer.   
     
     
       2. A magnetic recording element which comprises a nonmagnetic carrier having coated on at least one surface thereof a compressed solvent-free layer of finely divided magnetic pigment particles dispersed in a porous matrix containing a polymeric binder, lubricant, dispersing agent, and a porosity control agent selected from metal salts of carboxylic acids, nonionogenic diurethanes, calcium-containing micellar organic complexes and mixtures thereof, the pores of the layer having a diameter of 5-100 nm, a volume which is 5-50% of the volume of the compressed layer and surface area which is at least 100 times the free surface area of the exposed surface of the compressed layer.